This study was designed to compare the efficacy and safety of daily dapsone versus daily atovaquone suspension in the prevention of pneumocystis carinii pneumonia (pcp) amount HIV-infected patients at high risk for pcp and with a history of intolerance to trimethoprim and/or sulfonamides (tmp/smx, bacterium/sptra). The study was initiated in october 1995 and patients were followed to a common closing date of April 11, 1997. Pcp and vital status on this closing date were verified by clinical sites during April, May and June.